Astronauts aboard the U.S. space shuttle Endeavour have been testing the necessary systems in preparation for a landing early Wednesday in the southeastern state of Florida.
Commander Mark Kelly and his crew are aiming to touch down at 2:35 a.m., local time, 0635 UTC Wednesday at Kennedy Space Center.
Flight director Tony Ceccacci says the weather looks "very promising."
Endeavour has spent more than two weeks in space, delivering to the International Space Station a $2 billion cosmic ray detector, the Alpha Magnetic Spectrometer, and spare parts.
Wednesday's landing will end Endeavour's 19-year space career and mark the second of three U.S. shuttles to be retired. The U.S. space agency, NASA, says Endeavour flew a total of 198 million kilometers in its 25 missions.
The shuttle Atlantis is scheduled to blast into space in July, in the last mission of the 30-year U.S. shuttle program.
With the shuttle program ending, NASA will have to depend on space vehicles owned by other countries or by private industry to deliver supplies and crew to the International Space Station.
In addition to Mark Kelly, the six-member Endeavour crew includes Italian astronaut Roberto Vittori.
Kelly's wife, U.S. Congresswoman Gabrielle Giffords, is recovering from wounds suffered during a shooting in the state of Arizona in January.